1. Field of the Invention
The invention pertains to the field of optical transfer function analyzers.
An optical transfer function analyzer is a device for quantizing the resolving quality of an optical system. The optical transfer function analyzer measures the light scattered out of a bright beam into an area which should be unlighted. If E(x) is the illumination on an image surface of the analyzer as a function of position x, then the optical transfer function is found by taking the fourier sine-cosine transform pair of the derivative of E(x). The value of E is measured for successive positions until the data necessary for calculating the optical transfer function of the system being tested has been obtained.
2. Prior Art
Prior art optical transfer function analyzers employ mechanical scanning systems such as precise scanning of a razor edge or precise rotation of a drum containing a precision machined slot. These systems use mechanical scanning to control which element of the image controls the output of a photosensitive electrical output device, usually a photomultiplier tube - the output of the tube being representative of the light intensity at the selected image element. These systems have problems in that mechanical scanning systems do not provide completely reproducible scans. This prevents the use of repetitive scans to improve the signal to noise ratio of the values of E by integration (averaging) of the results for different scans. The accuracy of those systems which produce analog output plots is further deteriorated by the necessity of manually assigning digital values to the analog output plots in order to digitally calculate the optical transfer function of the system under test. Errors can arise during the assigning of values or in keypunching these values for delivery to a digital computer for calculation of the optical transfer function.
Further, since the calculations are not performed on line, more data than is necessary for simple pass/fail tests must be measured and the optical systems under test must be accurately identified with the resulting output plots in order to prevent the final data values from being credited to the wrong optical system.